Exposure to highly estrogenic substances can disrupt reproduction and increase cancer risk. Effects on bone metabolism and cardiovascular health also have been documented. Chemicals that are weakly estrogenic are widespread in the environment, including several pesticides and a variety of chemicals in plants. Health effects of these environmental estrogens are not known. As a first step in exploring this question, biological effects of plant estrogens will be measured in postmenopausal women. Ninety-four volunteers were recruited for the study, 68 of whom ate a diet rich in plant estrogens, and 26 of whom ate their usual diet. Urine, blood, and vaginal cells were collected for measurement of pituitary hormones, liver-produced plasma proteins, and estrogenization of vaginal cells. The field work is complete and specimens are currently being analyzed. If plant estrogens are found to be biologically active in postmenopausal women, further questions arise: (1) What effects do these chemicals have on other segments of the population: males, reproductively active women, and babies on soy formula? (2) Do effects of plant estrogens explain some of the differences in morbidity and mortality seen in vegetarians compared with nonvegetarians? (3) Can dietary changes be used in prevention or treatment of estrogen- related conditions? (4) Do other environmental estrogens (like pesticides) affect human health through estrogenic changes in human biology?